Stamping film, method for the production thereof and for transferring a label from said stamping film to a substrate

ABSTRACT

The invention relates to an embossing foil ( 100 ) for transferring labels ( 2 ) to documents of value ( 1 ). It comprises at least a carrier foil ( 10 ), a label layer ( 20 ) and an adhesion promoter layer ( 30 ). The dimensions of the adhesion promoter layer ( 30 ) are limited to the contour of the labels ( 2 ) to be transferred from the embossing foil ( 100 ).

[0001] This invention relates to the field of application of the labelsto any substrates, in particular optically variable security elements,such as holograms, to papers of value, such as bank notes. The inventionrelates specifically to a method for producing an embossing foilsuitable therefor, a corresponding embossing foil and a method fortransferring labels from said embossing foil to a substrate.

[0002] Applying labels to papers of value or any other objects serves toprotect products since the labels have special authenticity featuresthat are difficult to forge, such as holographic diffraction structures.For applying the labels to the particular substrates, numerous methodshave been proposed that have in common transferring the labels from atransfer foil to the substrate surface by an embossing die, usually ahot stamping die, whereby the transfer foil is regularly not transferredat the same time.

[0003] The basic structure of an embossing foil suitable therefor isdescribed in DE 26 49 479 B2 according to which a hot stamping foilconsists of a carrier foil to which at least one usually transparentlacquer layer is applied. Diffraction structures in the form of athree-dimensional relief pattern are then incorporated in the surface ofsaid lacquer layer by means of an engraved cylinder. The thus embossedlayer is covered with a thin metal layer to make the visual,diffractively acting, e.g. holographic, effect more distinctly visible.To permit a diffraction structure thus produced on the embossing foil tobe transferred to the substrate by the hot stamping method, the metallayer is provided with an adhesive layer or heat seal layer. Theadhesive layer of the hot stamping foil is then contacted with thesubstrate surface and its crosslinking induced by means of a hotstamping die from the back of the carrier foil. The adhesive producesbetween the substrate and the lacquer layer covered with the metal layera firm bond that is more stable than the adhesive forces acting betweenthe carrier foil and the lacquer layer. This effect can be additionallystrengthened by providing between the carrier foil and the lacquer layera separation layer that facilitates detachment of the layers from thecarrier foil. Additionally, an adhesion promoter layer can be providedbetween the lacquer layer covered with the metal layer and the adhesivelayer to improve the bond between adhesive layer and metal layer orsubstrate and label layers. As soon as the adhesive layer issufficiently crosslinked or dried, the carrier foil can be removed,whereby the label layers remain on the substrate in the area of theactivated adhesive layer. The form of the hot stamping die activatingthe adhesive layer thus determines the outline of the label transferredfrom the embossing foil.

[0004] There are different alternatives to this method, so that anordinary laminating cylinder can be used for example instead of aspecially formed embossing die. In such cases the adhesive layer isarranged so that only the desired area of the lacquer layer istransferred to the substrate. Thus, it is proposed for example in WO96/01187 to apply the adhesive layer to the hot stamping foil already inthe accordingly structured label form, whereby the lacquer layer canadditionally be provided on the carrier foil in a precise fit with thestructured adhesive layer for better contouring of the labels.

[0005] In contrast, WO 93/05124 and WO 92/20533 propose applying theadhesive layer directly to the substrate in the desired label form.

[0006] A further alternative is proposed in WO 93/16888 by which theadhesive layer is applied all over to the lacquer layer of the hotstamping foil, but the areas of said adhesive layer not to betransferred to the substrate are deactivated before the application stepby being accordingly masked with a fast drying resin ink.

[0007] However, all aforementioned methods have the disadvantage thatthe hot-melt adhesive layer is softened during transfer by the supply ofheat to make it adhesive, causing structured adhesive layers to spreadin the edge area thereof and unstructured, locally heated adhesivelayers to soften beyond the edge area of the local heating, so that inboth cases the transferred label lacks sharp contours.

[0008] A method by which sharply contoured labels can be transferredfrom a carrier foil to a substrate is described in DE 44 11 404.Therein, labels are produced directly on the carrier foil exactly in thelater desired outline form. However, such an embossing foil is hard towind onto storage rolls and therefore troublesome to handle.

[0009] DE 41 30 896 A1 describes another way of transferring clearlycontoured labels to the substrate. Here, the labels to be transferredare punched out while still located on the carrier foil, without thecarrier foil being damaged, and the areas of the label layer not to betransferred are removed from the carrier foil before the transferprocess. This method is expensive in terms of machinery.

[0010] The problem of the present invention is therefore to propose aneasily handled embossing foil that makes it possible to transfer sharplycontoured hologram labels to a substrate, in particular a bank note,without any special machinery expense.

[0011] A further problem of the invention is to propose correspondingmethods for producing such an embossing foil and for transferring alabel from such an embossing foil to a substrate.

[0012] These problems are solved according to the invention by thecombination of the features stated in the attached independent claims.Advantageous embodiments of the invention are stated in claims dependentthereon.

[0013] In contrast to the prior art, the invention provides forstructuring the label form by disposing an adhesion promoter layer incertain areas between the adhesive layer and the lacquer layeroptionally provided with a metal layer. That is, the adhesion promoterlayer is limited spatially to the dimensions of the single labels to bedetached from the label layer. The term “label layer” stands here forthe layer structure of a security element disposed continuously on acarrier layer. Said label layer preferably involves the conventionallayer structure of an embossed hologram. The invention can of coursealso be used for any other embossing foils from which structured labelswith a predetermined outline contour are transferred to a substrate.

[0014] The idea underlying the invention is to use bond forces ofdifferent strength between the adhesive layer and the label layer, onthe one hand, and the adhesive layer and the adhesion promoter layer, onthe other hand, as a point of break for exact-edge label application,because the adhesion between adhesive layer and adhesion promoter layeris higher than the adhesion between adhesive layer and directlyadjoining label layer. Moreover, the bond between carrier foil and labellayers is stronger than between adhesive layer and label layers. In thisway, only the areas of the label layers provided with the adhesionpromoter layer adhere to the substrate even when the adhesive layer isactivated all over. All other areas are removed with the carrier foil.

[0015] To be more independent in the choice of adhesive layer material,an alternative embodiment of the invention provides for filling theareas of the label layer not bearing the inventive adhesion promoterlayer with a separation layer. This supports the effect that a firm bondwith the adhesive layer arises only in the area of the adhesion promoterlayer, and moreover facilitates handling of the embossing foil since thelayer thickness of the embossing foil can thus be designed to beuniform.

[0016] The adhesive layer need not necessarily be part of the embossingfoil. It can also, or if needed also only additionally, be applieddirectly to the substrate. Furthermore, the adhesive layer can belimited to the specific areas of the labels to be transferred.

[0017] As explained above, the transfer of labels from the inventiveembossing foil does not require an exactly contoured embossing die. Theembossing die, which is preferably formed as a hot stamping die, shouldonly have a greater surface than the surface of the label to betransferred. In the projecting area of the die, no firm bond occursduring the application process between the label layer and the adhesivelayer or, in the case of the aforementioned alternative embodiment ofthe invention, between separation layer and adhesive layer. Due to theweight of the substrate firmly adhering to the label layer to betransferred in the area of the adhesion promoter layer, the label layertears along the outside edge of the adhesion promoter. Thus, only thedesired motif area of the label layer is applied to the substrate,whereas the label layer outside the desired motif area remains on thecarrier foil and is wound onto a waste roll with the carrier foil.

[0018] To achieve an easier tear, it may be expedient in somecircumstances to make lacquer layers present in the label layerstructure, such as an embossed lacquer layer, thinner outside thestructured motif area than in the motif area. To achieve easierdetachment of the label from the carrier foil, an additional separationlayer can further be provided between carrier foil and label layer.

[0019] The inventive embossing foil is simple to produce and easy tohandle. It can in particular be readily wound onto large storage rolls,in particular when all layers except the adhesion promoter layer areapplied to the carrier layer all over. The fluctuations in thickness ofthe adhesion promoter layer do not cause any problems during windingsince it constitutes only 1 to 3.5 percent of the total embossing foilthickness. When the areas between the adhesion promoter layer appliedonly in certain areas are filled with a separation layer, there areactually no fluctuations in thickness. In the other case, thefluctuations in thickness are partly compensated by the adhesive layerif the adhesive layer is part of the embossing foil and not applieddirectly to the substrate.

[0020] In the following, the invention will be described by way ofexample with reference to the Figure, in which:

[0021]FIG. 1 shows a bank note with an applied label in a top view,

[0022]FIG. 2 shows a cross section through an inventive embossing foilaccording to a first embodiment,

[0023]FIG. 3 shows a cross section through an inventive embossing foilaccording to a second embodiment, and

[0024]FIG. 4 shows a cross section through a bank note with appliedlabels.

[0025]FIG. 1 shows bank note 1 with label 2 applied thereto. FIG. 2shows in cross section hot stamping foil 100 from which label 2 isdetached and transferred to bank note 1. The embossing foil isconstructed as follows.

[0026] Carrier foil 10 bears label layer 20. Label layer 20 comprisestransparent lacquer layer 21 embossed on one side, and metal layer 22covering the embossed surface of lacquer layer 21. The embossed surfaceof lacquer layer 21 is formed as special three-dimensional relief 23 andacts as an optically variable, for example holographic, diffractionstructure whose optical impression is strengthened by metal layer 22.Label layer 20 is provided all over with hot-melt adhesive layer 40,with adhesion promoter layer 30 being provided in partial areas betweenlabel layer 20 and hot-melt adhesive layer 40.

[0027] The bond forces acting between adhesion promoter layer 30 andadhesive layer 40, on the one hand, and adhesion promoter layer 30 andthe label layer, on the other hand, are high compared to the bond forcesbetween label layer 20 and adhesive layer 40.

[0028] The contour of adhesion promoter layer 30 is selected here inaccordance with label 2 to be transferred.

[0029] The carrier foil preferably has a thickness of 10 to 40 microns.Metalized lacquer layer applied all over consists preferably of aUV-curable lacquer and preferably has a thickness of about 2 to 5microns. Adhesion promoter layer 30 has a thickness of about 0.5 to 1.5microns. And hot-melt adhesive layer 40 applied all over preferably hasa thickness of about 3 to 7 microns.

[0030] For applying single label 2 to bank note 1 or the endless banknote paper, adhesive layer 40 of embossing foil 100 is contacted withthe surface of bank note 1. Hot stamping die 50 transfers pressure andtemperature to hot-melt adhesive layer 40 from the back of hot stampingfoil 100 via carrier foil 10 and label layer 20. This causes the heatedarea of hot-melt adhesive 40 to first change to a liquid state andpenetrate partly into the surface of the bank note. After curing of theadhesive there is a firm bond between the bank note and label layer 20in the area of the adhesion promoter layer. Preferably, the surface ofhot stamping die 50 is formed somewhat greater than the individual areasof adhesion promoter layer 30 and protrudes accordingly beyond the outercontour of the areas of adhesion promoter layer 30, as shown in FIG. 2.

[0031] The firm bond between the bank note and the corresponding area ofadhesion promoter layer 30 produced by the curing of activated adhesivelayer 40, and the firm bond between adhesion promoter layer 30 and labellayer 20, cause embossed lacquer layer 21 with thin metal layer 22 totear off along the outside edge of adhesion promoter 30 when carrierfoil 10 is removed from bank note 1.

[0032] However, the tear of embossed lacquer layer 21 with metal layer22 presupposes that the bond between adhesive layer 40 likewiseactivated in the edge area of adhesion promoter layer 30 issubstantially weaker than in the area of adhesion promoter layer 30. Ifthis precondition is not given due to the adhesive material used, it isadvantageous to fill the spaces between the individual areas of adhesionpromoter layer 30 with separating agent material forming separationlayer 31, as shown in FIG. 3. Instead of an embossing die, acontinuously working web-fed embossing machine can also be used, sincethe label layer is transferred to the substrate according to theinvention only in the areas provided with the adhesion promoter layer.

[0033] The embodiment of the invention shown in FIG. 3 differs from theembodiment shown in FIG. 2 in addition by the following two features,which can be realized just the same individually or jointly in theembodiment according to FIG. 2 in corresponding fashion.

[0034] Thus, metal layer 22 is not provided on lacquer layer 21 all overbut only in those areas that are part of the label to be transferred.Said areas are completely covered by adhesion promoter layer 30, so thatmetal layer 22 is completely protected from environmental influences.

[0035] In addition, it is provided in the embodiment according to FIG. 3that metal layer 22 has gaps 24 that can represent characters, patternsor the like. Bank note 1 or the bank note material is not shown here.

[0036]FIG. 4 shows bank note 1 shown in FIG. 1 in cross section alongA-A, the transferred label having layer structure 20 shown in FIG. 2.Transfer foil 10 of hot stamping foil 100 shown in FIG. 2 was removedafter transfer of label 2 and wound onto a waste roll with thecomponents of the embossing foil not transferred. In addition, it can beseen, shown by dots, that adhesive components of adhesive layer 40 havepenetrated into the surface of bank note 1, also in the area outside theouter contour of adhesion promoter layer 30.

1. A method for producing an embossing foil (100) with a label layer (20) for later transfer of single labels (2) to a substrate (1) comprising the following steps: providing a carrier foil (10) with a label layer (20) from which the single labels (2) are later to be detached, applying an adhesion promoter layer (30) to the label layer (20) for producing a stable bond between the label layer (20) and an adhesive layer (40), characterized in that the adhesion promoter layer (30) is limited spatially to the dimensions of the single labels (2) later to be detached.
 2. A method for transferring a label (2) from an embossing foil (100) to a substrate (1) comprising the following steps: providing an embossing foil (100) with a label layer (20) from which single labels (2) are subsequently detached, and an adhesion promoter layer (30) applied to the label layer (20), the adhesion promoter layer being limited spatially to the dimensions of the single labels (2) to be subsequently detached, applying an adhesive layer to the adhesion promoter layer (30) or to the substrate (1) if the embossing foil (100) is not already equipped with such an adhesive layer (40), contacting the embossing foil (100) with the substrate (1) in the area of the adhesive layer (40), and detaching a label (2) from the label layer (20) and transferring the label (2) to the substrate (1) in an embossing operation.
 3. A method according to claim 1 or 2, characterized in that the adhesive layer (40) is applied to the adhesion promoter layer (30).
 4. A method according to claim 3, characterized in that the adhesive layer (40) is applied all over to the adhesion promoter layer (30) and areas of the label layer (20) located therebetween.
 5. A method according to claim 3, characterized in that the adhesive layer (40) is applied partially and at least to the adhesion promoter layer (30).
 6. A method according to any of claims 1 to 5, characterized in that areas located between the adhesion promoter layer (30) applied to the label layer in spatially limited fashion are filled with a separation layer (31).
 7. A method according to any of claims 1 to 6, characterized in that the adhesive layer consists of a hot-melt adhesive, and the embossing operation is effected by means of a hot stamping die whose die surface is greater than the dimensions of the labels (2) to be detached.
 8. A method according to any of claims 1 to 7, characterized in that the label layer (20) has diffraction structures in the form of a relief (23).
 9. A method according to claim 8, characterized in that the diffraction structures are provided at least partially with a metalization (22).
 10. A method according to claim 9, characterized in that the metalization (22) has gaps (21) in the form of characters, patterns or the like.
 11. A method for producing a document of value, characterized in that a label (2) is transferred to the document of value according to claim 2 or according to any of claims 3 to 10 with 2, the document of value itself forming the substrate (1).
 12. A method according to claim 11, characterized in that the document of value is a bank note.
 13. An embossing foil comprising: a carrier foil (10), a label layer (20) on the carrier foil (10) from which single labels (2) are detachable, and an adhesion promoter layer (30) on the label layer (20) for producing a stable bond between the label layer (20) and an adhesive layer (40), characterized in that the adhesion promoter layer (30) is provided on the label layer (20) in spaced-apart areas.
 14. An embossing foil according to claim 13, characterized in that an adhesive layer (40) is applied to the adhesion promoter layer (30).
 15. An embossing foil according to claim 14, characterized in that the adhesive layer (40) is applied all over to the adhesion promoter layer (30) and areas of the label layer (20) located therebetween.
 16. An embossing foil according to claim 14, characterized in that the adhesive layer (40) is applied partially and at least to the adhesion promoter layer (30).
 17. An embossing foil according to any of claims 13 to 16, characterized in that the areas between the areas of the adhesion promoter layer (30) provided spaced-apart on the label layer (20) are filled with a separation layer (31).
 18. An embossing foil according to any of claims 13 to 17, characterized in that the adhesive layer (40) is a hot-melt adhesive layer.
 19. An embossing foil according to any of claims 13 to 18, characterized in that the label layer (20) has diffraction structures in the form of a relief (23).
 20. An embossing foil according to claim 19, characterized in that the diffraction structures are provided at least partially with a metalization (22).
 21. An embossing foil according to claim 20, characterized in that the metalization (22) has gaps (24) in the form of characters, patterns or the like. 